Defect detection in a point cloud

ABSTRACT

Examples described herein provide a method that includes performing a first scan of an object to generate first scan data. The method further includes detecting a defect on a surface of the object by analyzing the first scan data to identify a region of interest containing the defect by comparing the first scan data to reference scan data. The method further includes performing a second scan of the region of interest containing the defect to generate second scan data, the second scan data being higher resolution scan data than the first scan data. The method further includes combining the first scan data and the second scan data to generate a point cloud of the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 63/230,360 filed Aug. 6, 2021, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Embodiments of the present disclosure generally relate to detecting defects in a point cloud.

The acquisition of three-dimensional coordinates of an object or an environment is known. Various techniques may be used, such as time-of-flight (TOF) or triangulation methods, for example. A TOF system such as a laser tracker, for example, directs a beam of light such as a laser beam toward a retroreflector target positioned over a spot to be measured. An absolute distance meter (ADM) is used to determine the distance from the distance meter to the retroreflector based on the length of time it takes the light to travel to the spot and return. By moving the retroreflector target over the surface of the object, the coordinates of the object surface may be ascertained. Another example of a TOF system is a laser scanner that measures a distance to a spot on a diffuse surface with an ADM that measures the time for the light to travel to the spot and return. TOF systems have advantages in being accurate, but in some cases may be slower than systems that project a pattern such as a plurality of light spots simultaneously onto the surface at each instant in time.

In contrast, a triangulation system, such as a scanner, projects either a line of light (e.g., from a laser line probe) or a pattern of light (e.g., from a structured light) onto the surface. In this system, a camera is coupled to a projector in a fixed mechanical relationship. The light/pattern emitted from the projector is reflected off of the surface and detected by the camera. Since the camera and projector are arranged in a fixed relationship, the distance to the object may be determined from captured images using trigonometric principles. Triangulation systems provide advantages in quickly acquiring coordinate data over large areas.

In some systems, during the scanning process, the scanner acquires, at different times, a series of images of the patterns of light formed on the object surface. These multiple images are then registered relative to each other so that the position and orientation of each image relative to the other images are known. Where the scanner is handheld, various techniques have been used to register the images. One common technique uses features in the images to match overlapping areas of adjacent image frames. This technique works well when the object being measured has many features relative to the field of view of the scanner. However, if the object contains a relatively large flat or curved surface, the images may not properly register relative to each other.

Accordingly, while existing 3D scanners are suitable for their intended purposes, what is needed is a 3D scanner having certain features of one or more embodiments of the present invention.

SUMMARY

Embodiments of the present invention are directed to defect detection in a point cloud.

According to one or more examples, a method is provided that includes performing a first scan of an object to generate first scan data. The method further includes detecting a defect on a surface of the object by analyzing the first scan data to identify a region of interest containing the defect by comparing the first scan data to reference scan data. The method further includes performing a second scan of the region of interest containing the defect to generate second scan data, the second scan data being higher resolution scan data than the first scan data. The method further includes combining the first scan data and the second scan data to generate a point cloud of the object.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the first scan is performed using a first scanner, and the second scan is performed using the first scanner.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include, prior to performing the second scan using the first scanner, decreasing a distance between the first scanner and the object.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the first scan is performed using a first scanner, and that the second scan is performed using a second scanner.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the object is moved passed the first scanner at a first speed while performing the first scan, and the object is moved passed the second scanner at a second speed while performing the second scan, the second speed being slower than the first speed.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the object is a first distance from the first scanner when the first scan is performed and a second distance from the second scanner when the second scan is performed, the first distance being greater than the second distance.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the first scanner is a first type of scanner, and the second scanner is a second type of scanner different than the first type of scanner.

According to one or more examples, a method is provided that includes performing a scan of an object of interest to generate scan data. The method further includes detecting a defect on a surface of the object by analyzing the scan data to identify a region of interest containing the defect by comparing the scan data to reference scan data. The method further includes upscaling a subset of the scan data associated with the region of interest containing the defect to generate upscaled scan data. The method further includes combining the scan data and the upscaled scan data to generate a point cloud of the object.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the upscaling includes: performing, by a processing device, using a neural network, pattern recognition on the subset of the scan data to recognize a feature in the subset of the scan data; and performing, by the processing device, upscaling of the subset of the scan data to increase a resolution of the subset of the scan data while maintaining the feature to generate the upscaled scan data.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include training the neural network, using a training set of images, to perform the pattern recognition and the upscaling.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that each set of the training set of images includes an original image of a laser projection pattern and a downscaled image of the laser projection pattern.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the training further includes comparing the downscaled image to the original image.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the processing device is disposed in a three-dimensional scanner such that performing the pattern recognition and performing the upscaling are performed by the three-dimensional scanner.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the neural network includes an encoder and a decoder.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the neural network utilizes a long short-term memory.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that the feature is at least one of a pattern, a color, or a shape.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include: training a neural network to perform upscaling the scan data captured by a three-dimensional triangulation scanner; capturing the scan data using the three-dimensional triangulation scanner; performing, using the neural network, pattern recognition on the scan data; and performing, using the neural network, upscaling on the scan data without manipulating image data associated with the scan data to generate an upscaled image.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that capturing the image includes scanning, by the three-dimensional triangulation scanner, an environment.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that training the neural network includes using a training set of images.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method include that each set of the training set of images includes an original image of a laser projection pattern and a downscaled image of the laser projection pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of embodiments of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts a system for scanning an environment according to one or more embodiments described herein;

FIG. 2 depicts an example image of a laser projection pattern according to one or more embodiments described herein;

FIG. 3 depicts a portion of the image of FIG. 2 showing a laser dot that has been enlarged according to one or more embodiments described herein;

FIG. 4 depicts the portion from FIG. 3 after upscaling has been applied according to one or more embodiments described herein;

FIG. 5 depicts a flow diagram of a method for upscaling triangulation scanner images to reduce noise according to one or more embodiments described herein;

FIGS. 6A and 6B depict an autoencoder according to one or more embodiments described herein;

FIGS. 7, 8, 9, 10, and 11 are isometric, partial isometric, partial top, partial front, and second partial top views, respectively, of a triangulation scanner according to one or more embodiments described herein;

FIG. 12A is a schematic view of a triangulation scanner having a projector, a first camera, and a second camera according to one or more embodiments described herein;

FIG. 12B is a schematic representation of a triangulation scanner having a projector that projects and uncoded pattern of uncoded spots, received by a first camera, and a second camera according to one or more embodiments described herein;

FIG. 12C is an example of an uncoded pattern of uncoded spots according to one or more embodiments described herein;

FIG. 12D is a representation of one mathematical method that might be used to determine a nearness of intersection of three lines according to one or more embodiments described herein;

FIG. 12E is a list of elements in a method for determining 3D coordinates of an object according to one or more embodiments described herein;

FIG. 13 is an isometric view of a triangulation scanner having a projector and two cameras arranged in a triangle according to one or more embodiments described herein;

FIG. 14 is a schematic illustration of intersecting epipolar lines in epipolar planes for a combination of projectors and cameras according to one or more embodiments described herein;

FIGS. 15A, 15B, 15C, 15D, 15E are schematic diagrams illustrating different types of projectors according to one or more embodiments described herein;

FIG. 16A is an isometric view of a triangulation scanner having two projectors and one camera according to one or more embodiments described herein;

FIG. 16B is an isometric view of a triangulation scanner having three cameras and one projector according to one or more embodiments described herein;

FIG. 16C is an isometric view of a triangulation scanner having one projector and two cameras and further including a camera to assist in registration or colorization according to one or more embodiments described herein;

FIG. 17A illustrates a triangulation scanner used to measure an object moving on a conveyor belt according to one or more embodiments described herein;

FIG. 17B illustrates a triangulation scanner moved by a robot end effector, according to one or more embodiments described herein;

FIG. 18 illustrates front and back reflections off a relatively transparent material such as glass according to one or more embodiments described herein;

FIGS. 19A and 19B depict a modular inspection system according to one or more embodiments described herein;

FIGS. 20A and 20B depicts block diagrams of systems for defect detection according to one or more embodiments described herein;

FIG. 21 depicts a flow diagram of a method for defect detection according to one or more embodiments described herein;

FIG. 22 depicts a flow diagram of a method for defect detection according to one or more embodiments described herein; and

FIG. 23 depicts a flow diagram of a method for defect detection according to one or more embodiments described herein.

DETAILED DESCRIPTION

The technical solutions described herein generally relate to techniques for detecting defects on a surface of an object being scanned. A three-dimensional (3D) scanning device or “scanner” as depicted in FIG. 1 can be used to generate 3D points (referred to as a “point cloud”). The point cloud can be analyzed to detect defects on the surface of the object.

In particular, FIG. 1 depicts a system 100 for scanning an environment according to one or more embodiments described herein. The system 100 includes a computing device 110 coupled with a scanner 120, which can be a 3D scanner or another suitable scanner. The coupling facilitates wired and/or wireless communication between the computing device 110 and the scanner 120. The scanner 120 includes a set of sensors 122. The set of sensors 122 can include different types of sensors, such as LIDAR sensor 122A (light detection and ranging), RGB-D camera 122B (red-green-blue-depth), and wide-angle/fisheye camera 122C, and other types of sensors. The scanner 120 can also include an inertial measurement unit (IMU) 126 to keep track of a 3D movement and orientation of the scanner 120. The scanner 120 can further include a processor 124 that, in turn, includes one or more processing units. The processor 124 controls the measurements performed using the set of sensors 122. In one or more examples, the measurements are performed based on one or more instructions received from the computing device 110. In an embodiment, the LIDAR sensor 122A is a two-dimensional (2D) scanner that sweeps a line of light in a plane (e.g. a plane horizontal to the floor).

According to one or more embodiments described herein, the scanner 120 is a dynamic machine vision sensor (DMVS) scanner manufactured by FARO® Technologies, Inc. of Lake Mary, Florida, USA. DMVS scanners are discussed further with reference to FIGS. 11A-19B. In an embodiment, the scanner 120 may be that described in commonly owned United States Patent Publication 2018/0321383 entitled Triangulation Scanner having Flat Geometry and Projecting Uncoded Spots, the contents of which are incorporated by reference herein. It should be appreciated that the techniques described herein are not limited to use with DMVS scanners and that other types of 3D scanners can be used.

The computing device 110 can be a desktop computer, a laptop computer, a tablet computer, a phone, or any other type of computing device that can communicate with the scanner 120.

In one or more embodiments, the computing device 110 generates a point cloud 130 (e.g., a 3D point cloud) of the environment being scanned by the scanner 120 using the set of sensors 122. The point cloud 130 is a set of data points (i.e., a collection of three-dimensional coordinates) that correspond to surfaces of objects in the environment being scanned and/or of the environment itself. According to one or more embodiments described herein, a display (not shown) displays a live view of the point cloud 130.

Turning now to an overview of technologies that are more specifically relevant to one or more embodiments described herein, triangulation scanners (see, e.g., the scanner 120 of FIG. 1 and/or the triangulation scanner 1101 of FIGS. 11A-11E) generally include at least one projector and at least one camera. The projector and camera are separated by a baseline distance. Images of the laser projection pattern are used to generate 3D points. An example image 200 of a laser projection pattern is depicted in FIG. 2 . Due to the nature of triangulation scanners, 3D data is typically very noise on longer distances.

For scanners such as the triangulation scanner 1101, a typical 2-sigma noise might be 500 μm at a 500 mm measurement distance. In some applications, sensitivity for finding defects may be less than the 2-sigma noise (e.g., less than 500 m such as about 300 m). This prevent can prevent the use of such scanners for certain applications. The reason for this is a combination of camera and laser noise. For camera noise, pixel size plays an important role. For example, FIG. 3 depicts a portion 300 of the image 200 of FIG. 3 showing a laser dot 302 that has been enlarged. In this example, the portion 300 is enlarged by about 1300%, although this enlargement amount is not intended to be limited and is only exemplary. As can be seen, the laser dot 302 is pixelated, and the individual pixels are easy to identify. To minimize this effect, pixel size must be decreased. To do this, the image 200 is upscaled as shown in FIG. 4 . This can be accomplished in various ways, including by replacing the camera of the scanner with a model that captures images in a higher resolution or by upscaling the image in software.

Substituting or replacing the camera in a scanner is a financially expensive approach, and upscaling the image in software is a computationally expensive approach. Upscaling using conventional techniques is computational expensive driven largely by interpolating between the pixels. For example, in FIG. 4 , an off-the-shelf photo editing application was used to perform the upscaling on the image 200 to generate the portion 400. However, when using triangulation scanners such as a DMVS (which captures images, for example, at about 70 Hz), high performance is desired, and generating 3D data occupies a large amount of processing time. Upscaling and interpolating the images using conventional algorithm-based techniques would have a large negative impact on the processing time and thus impact the image capture speed, which would be reduced undesirably. The embodiments described herein provide for software-based upscaling without reducing image capture speed of the scanner by using artificial intelligence to upscale and interpolate images.

FIG. 5 depicts a flow diagram of a method 500 for upscaling triangulation scanner images to reduce noise according to one or more embodiments described herein. The method 500 can be performed by any suitable processing system, processing device, scanner, etc. such as the processing systems, processing devices, and scanners described herein. For example, the processor 124 is disposed in a three-dimensional scanner (e.g., the scanner 120) such that performing the image recognition and performing the upscaling are performed by the three-dimensional scanner.

According to one or more embodiments described herein, the techniques for upscaling triangulation scanner images provided herein are a fully automated process that uses machine learning to perform pattern recognition and determine how edges and shapes within an image should look while increasing the overall size of an image. This process has been trained on large datasets, allowing it to accurately clear up images. In particular, the image data is not manipulated; rather the patterns, colors, and shapes in the image are recognized. This is referred to as a “raw data pattern.” After the raw data pattern is recognized in the image, a neural network is applied to deconvolute the pixel intensity. If this were performed conventionally, in a larger image with blurry edges and colors would result (see, e.g., FIG. 3 ). However, by training a neural network to perform the deconvolution only on the rasterization of the image, the real image is maintained and enhanced by presenting it better to the user and/or for further processing. This results in more pixels to work with and unmanipulated data, which in turns improves precision, such as for a laser raster to map point-to-pixel approach. Accordingly, faster and better results are achieved. The method 500 is now described in more detail.

At block 502, a neural network is trained to perform image upscaling on images captured by a 3D triangulation scanner (e.g., the scanner 120 of FIG. 1 , the triangulation scanner 1101 of FIGS. 7, 8, 9, 10, and 11 , etc.). As described herein, a neural network can be trained to perform image upscaling, which is useful for reducing noise in scanned images, for example. More specifically, the present techniques can incorporate and utilize rule-based decision making and artificial intelligence (AI) reasoning to accomplish the various operations described herein, namely upscaling images, such as scanned images from triangulation scanners. The phrase “machine learning” broadly describes a function of electronic systems that learn from data. A machine learning system, engine, or module can include a trainable machine learning algorithm that can be trained, such as in an external cloud environment, to learn functional relationships between inputs and outputs that are currently unknown, and the resulting model can be used for automatically upscaling images. In one or more embodiments, machine learning functionality can be implemented using an artificial neural network (ANN) having the capability to be trained to perform a currently unknown function. In machine learning and cognitive science, ANNs are a family of statistical learning models inspired by the biological neural networks of animals, and in particular the brain. ANNs can be used to estimate or approximate systems and functions that depend on a large number of inputs. Convolutional neural networks (CNN) are a class of deep, feed-forward ANN that are particularly useful at analyzing visual imagery.

ANNs can be embodied as so-called “neuromorphic” systems of interconnected processor elements that act as simulated “neurons” and exchange “messages” between each other in the form of electronic signals. Similar to the so-called “plasticity” of synaptic neurotransmitter connections that carry messages between biological neurons, the connections in ANNs that carry electronic messages between simulated neurons are provided with numeric weights that correspond to the strength or weakness of a given connection. The weights can be adjusted and tuned based on experience, making ANNs adaptive to inputs and capable of learning. For example, an ANN for handwriting recognition is defined by a set of input neurons that can be activated by the pixels of an input image. After being weighted and transformed by a function determined by the network's designer, the activation of these input neurons are then passed to other downstream neurons, which are often referred to as “hidden” neurons. This process is repeated until an output neuron is activated. The activated output neuron determines which character was read. It should be appreciated that these same techniques can be applied in the case of upscaling images.

To train the neural network, set of images (referred to as a training set of images) are created using, for example, a photo editing application. The training set of images includes pairs of images: an original image of a laser projection pattern and a downscaled image of the laser projection pattern. The downscaled image is a manually worsened version of the original image. For example, if the original image is a 1024×1024 image, the downscaled image is manually worsened to 256×256 and is then compared against the original image.

A neural network can be designed with a given depth and architecture particular to a specific scanner, such as a DMVS or other suitable scanner. According to one or more embodiments described herein, an autoencoder and autodecoder technique is applied with an intermediate long short-term memory (LSTM) layer chain between the encoding and decoding blocks. For example, FIGS. 6A and 6B depict an autoencoder 602 that implements machine learning according to one or more embodiments described herein. As shown in FIG. 6A, the autoencoder 602 receives a scanned image 601 as an input and produces an upscaled image 603 as an output. An autoencoder, such as the autoencoder 602, uses a neural network that learns in an unsupervised way. Autoencoders can be used in a variety of applications, such as dimensionality reduction, anomaly detection, denoising, etc. According to one or more embodiments described herein, the autoencoder 602 can be trained to recognize certain information in input data (e.g., the scanned image 601). As one example, an autoencoder can be trained to recognize real information, such as handwriting, in a noisy image and to produce the recognized information without surrounding noise as an upscaled image (e.g., the upscaled image 603). In examples, the output is a binarized image or an image that is capable of being binarized. An autoencoder can be trained to find real information in images with different segments with different gray value levels and process this segment information.

FIG. 6B depicts the autoencoder 602 in more detail. In this example, the autoencoder 602 includes an encoder 610 that receives the scanned image 601 and a decoder 620 that produces the upscaled image 603. The encoder 610 includes an input layer 611 (labeled as “X”), and the decoder 620 includes an output layer 621 (labeled as “X′”). The input layers 611 and the output layer 621 use an activation function, which may be non-linear. An example of an activation function is a rectified linear unit (ReLU). Each of the encoder 610 and the decoder 620 utilizes code 630 (labeled as “h”) in a latent space between the input layer 611 and the output layer 621 to perform denoising. In some examples, the code 630 can include the intermediate LSTM layer chain between the encoding and decoding blocks.

In an example, the neural network is trained all around purposes. That is, a model can be trained on images/data from multiple sources (e.g., customers) to produce a general model applicable across multiple data sets. In another example, the neural network is trained for a particular scanning implementation, which may be a perfect fit for a particular customer based on that customer's images/data, since the trained model is a perfect fit for the customer's particular environment/use.

After the neural network is trained, it can be used as an evaluation script to evaluate scanned images from the scanner. The scanned images, which include a laser pattern, are upscaled using the trained neural network. The benefit of this approach is high precision, taken into consideration that the overhead created in the chain by the upscaling step can be done in real-time or near-real-time. For example, at block 504 of the method 500, the 3D triangulation scanner captures an image as described herein. Once the image is captured, the trained neural network is applied to upscale the image at block 506 and 506.

Particularly, at block 506, the image is input into the neural network, and the neural network performs pattern recognition on the image. This can include recognizing a pattern, a color, a shape, etc. in the image. For example, in FIG. 2 , the laser dot 302 is recognized as having a circular shape. At block 508, the neural network is used to perform upscaling of the image to increase the resolution of the image while maintaining the pattern, color, shape, etc. of the original image to generate an upscaled image (see, e.g., FIG. 5 ). As shown in FIG. 5 , the upscaled image is a higher resolution compared to a non-upscaled image (see, e.g., FIG. 4 ).

Additional processes also may be included, and it should be understood that the process depicted in FIG. 5 represents an illustration, and that other processes may be added or existing processes may be removed, modified, or rearranged without departing from the scope of the present disclosure.

Turning now to FIG. 7 , it may be desired to capture three-dimensional (3D) measurements of objects. For example, the point cloud 130 of FIG. 1 may be captured by the scanner 120. One such example of the scanner 120 is now described. Such example scanner is referred to as a DVMS scanner by FARO®.

In an embodiment illustrated in FIGS. 7, 8, 9, 10, and 11 , a triangulation scanner 1101 includes a body 1105, a projector 1120, a first camera 1130, and a second camera 1140. In an embodiment, the projector optical axis 1122 of the projector 1120, the first-camera optical axis 1132 of the first camera 1130, and the second-camera optical axis 1142 of the second camera 1140 all lie on a common plane 1150, as shown in FIGS. 9, 10 . In some embodiments, an optical axis passes through a center of symmetry of an optical system, which might be a projector or a camera, for example. For example, an optical axis may pass through a center of curvature of lens surfaces or mirror surfaces in an optical system. The common plane 1150, also referred to as a first plane 1150, extends perpendicular into and out of the paper in FIG. 10 .

In an embodiment, the body 1105 includes a bottom support structure 1106, a top support structure 1107, spacers 1108, camera mounting plates 1109, bottom mounts 1110, dress cover 1111, windows 1112 for the projector and cameras, Ethernet connectors 1113, and GPIO connector 1114. In addition, the body includes a front side 1115 and a back side 1116. In an embodiment, the bottom support structure 1106 and the top support structure 1107 are flat plates made of carbon-fiber composite material. In an embodiment, the carbon-fiber composite material has a low coefficient of thermal expansion (CTE). In an embodiment, the spacers 1108 are made of aluminum and are sized to provide a common separation between the bottom support structure 1106 and the top support structure 1107.

In an embodiment, the projector 1120 includes a projector body 1124 and a projector front surface 1126. In an embodiment, the projector 1120 includes a light source 1125 that attaches to the projector body 1124 that includes a turning mirror and a diffractive optical element (DOE), as explained herein below with respect to FIGS. 15A, 15B, 15C. The light source 1125 may be a laser, a superluminescent diode, or a partially coherent LED, for example. In an embodiment, the DOE produces an array of spots arranged in a regular pattern. In an embodiment, the projector 1120 emits light at a near infrared wavelength.

In an embodiment, the first camera 1130 includes a first-camera body 1134 and a first-camera front surface 36. In an embodiment, the first camera includes a lens, a photosensitive array, and camera electronics. The first camera 1130 forms on the photosensitive array a first image of the uncoded spots projected onto an object by the projector 1120. In an embodiment, the first camera responds to near infrared light.

In an embodiment, the second camera 1140 includes a second-camera body 1144 and a second-camera front surface 1146. In an embodiment, the second camera includes a lens, a photosensitive array, and camera electronics. The second camera 1140 forms a second image of the uncoded spots projected onto an object by the projector 1120. In an embodiment, the second camera responds to light in the near infrared spectrum. In an embodiment, a processor 1102 is used to determine 3D coordinates of points on an object according to methods described herein below. The processor 1102 may be included inside the body 1105 or may be external to the body. In further embodiments, more than one processor is used. In still further embodiments, the processor 1102 may be remotely located from the triangulation scanner.

FIG. 11 is a top view of the triangulation scanner 1101. A projector ray 1128 extends along the projector optical axis from the body of the projector 1120 through the projector front surface 1126. In doing so, the projector ray 1128 passes through the front side 1115. A first-camera ray 1138 extends along the first-camera optical axis 1132 from the body of the first camera 1130 through the first-camera front surface 1136. In doing so, the front-camera ray 1138 passes through the front side 1115. A second-camera ray 1148 extends along the second-camera optical axis 1142 from the body of the second camera 1130 through the second-camera front surface 1146. In doing so, the second-camera ray 1148 passes through the front side 1115.

FIG. 12A shows elements of a triangulation scanner 1200 a that might, for example, be the triangulation scanner 1101 shown in FIGS. 7-11 . In an embodiment, the triangulation scanner 1200 a includes a projector 1250, a first camera 1210, and a second camera 1230. In an embodiment, the projector 1250 creates a pattern of light on a pattern generator plane 1252. An exemplary corrected point 1253 on the pattern projects a ray of light 1251 through the perspective center 1258 (point D) of the lens 1254 onto an object surface 1270 at a point 1272 (point F). The point 1272 is imaged by the first camera 1210 by receiving a ray of light from the point 1272 through the perspective center 1218 (point E) of the lens 1214 onto the surface of a photosensitive array 1212 of the camera as a corrected point 1220. The point 1220 is corrected in the read-out data by applying a correction value to remove the effects of lens aberrations. The point 1272 is likewise imaged by the second camera 1230 by receiving a ray of light from the point 1272 through the perspective center 1238 (point C) of the lens 1234 onto the surface of the photosensitive array 1232 of the second camera as a corrected point 1235. It should be understood that as used herein any reference to a lens includes any type of lens system whether a single lens or multiple lens elements, including an aperture within the lens system. It should be understood that any reference to a projector in this document refers not only to a system projecting with a lens or lens system an image plane to an object plane. The projector does not necessarily have a physical pattern-generating plane 1252 but may have any other set of elements that generate a pattern. For example, in a projector having a DOE, the diverging spots of light may be traced backward to obtain a perspective center for the projector and also to obtain a reference projector plane that appears to generate the pattern. In most cases, the projectors described herein propagate uncoded spots of light in an uncoded pattern. However, a projector may further be operable to project coded spots of light, to project in a coded pattern, or to project coded spots of light in a coded pattern. In other words, in some aspects of the disclosed embodiments, the projector is at least operable to project uncoded spots in an uncoded pattern but may in addition project in other coded elements and coded patterns.

In an embodiment where the triangulation scanner 1200 a of FIG. 12A is a single-shot scanner that determines 3D coordinates based on a single projection of a projection pattern and a single image captured by each of the two cameras, then a correspondence between the projector point 1253, the image point 1220, and the image point 1235 may be obtained by matching a coded pattern projected by the projector 1250 and received by the two cameras 1210, 1230. Alternatively, the coded pattern may be matched for two of the three elements—for example, the two cameras 1210, 1230 or for the projector 1250 and one of the two cameras 1210 or 1230. This is possible in a single-shot triangulation scanner because of coding in the projected elements or in the projected pattern or both.

After a correspondence is determined among projected and imaged elements, a triangulation calculation is performed to determine 3D coordinates of the projected element on an object. For FIG. 12A, the elements are uncoded spots projected in a uncoded pattern. In an embodiment, a triangulation calculation is performed based on selection of a spot for which correspondence has been obtained on each of two cameras. In this embodiment, the relative position and orientation of the two cameras is used. For example, the baseline distance B3 between the perspective centers 1218 and 1238 is used to perform a triangulation calculation based on the first image of the first camera 1210 and on the second image of the second camera 1230. Likewise, the baseline B1 is used to perform a triangulation calculation based on the projected pattern of the projector 1250 and on the second image of the second camera 1230. Similarly, the baseline B2 is used to perform a triangulation calculation based on the projected pattern of the projector 1250 and on the first image of the first camera 1210. In an embodiment, the correspondence is determined based at least on an uncoded pattern of uncoded elements projected by the projector, a first image of the uncoded pattern captured by the first camera, and a second image of the uncoded pattern captured by the second camera. In an embodiment, the correspondence is further based at least in part on a position of the projector, the first camera, and the second camera. In a further embodiment, the correspondence is further based at least in part on an orientation of the projector, the first camera, and the second camera.

The term “uncoded element” or “uncoded spot” as used herein refers to a projected or imaged element that includes no internal structure that enables it to be distinguished from other uncoded elements that are projected or imaged. The term “uncoded pattern” as used herein refers to a pattern in which information is not encoded in the relative positions of projected or imaged elements. For example, one method for encoding information into a projected pattern is to project a quasi-random pattern of “dots” in which the relative position of the dots is known ahead of time and can be used to determine correspondence of elements in two images or in a projection and an image. Such a quasi-random pattern contains information that may be used to establish correspondence among points and hence is not an example of a uncoded pattern. An example of an uncoded pattern is a rectilinear pattern of projected pattern elements.

In an embodiment, uncoded spots are projected in an uncoded pattern as illustrated in the scanner system 12100 of FIG. 12B. In an embodiment, the scanner system 12100 includes a projector 12110, a first camera 12130, a second camera 12140, and a processor 12150. The projector projects an uncoded pattern of uncoded spots off a projector reference plane 12114. In an embodiment illustrated in FIGS. 12B and 12C, the uncoded pattern of uncoded spots is a rectilinear array 12111 of circular spots that form illuminated object spots 12121 on the object 12120. In an embodiment, the rectilinear array of spots 12111 arriving at the object 12120 is modified or distorted into the pattern of illuminated object spots 12121 according to the characteristics of the object 12120. An exemplary uncoded spot 12112 from within the projected rectilinear array 12111 is projected onto the object 12120 as a spot 12122. The direction from the projector spot 12112 to the illuminated object spot 12122 may be found by drawing a straight line 12124 from the projector spot 12112 on the reference plane 12114 through the projector perspective center 12116. The location of the projector perspective center 12116 is determined by the characteristics of the projector optical system.

In an embodiment, the illuminated object spot 12122 produces a first image spot 12134 on the first image plane 12136 of the first camera 12130. The direction from the first image spot to the illuminated object spot 12122 may be found by drawing a straight line 12126 from the first image spot 12134 through the first camera perspective center 12132. The location of the first camera perspective center 12132 is determined by the characteristics of the first camera optical system.

In an embodiment, the illuminated object spot 12122 produces a second image spot 12144 on the second image plane 12146 of the second camera 12140. The direction from the second image spot 12144 to the illuminated object spot 12122 may be found by drawing a straight line 12126 from the second image spot 12144 through the second camera perspective center 12142. The location of the second camera perspective center 12142 is determined by the characteristics of the second camera optical system.

In an embodiment, a processor 12150 is in communication with the projector 12110, the first camera 12130, and the second camera 12140. Either wired or wireless channels 12151 may be used to establish connection among the processor 12150, the projector 12110, the first camera 12130, and the second camera 12140. The processor may include a single processing unit or multiple processing units and may include components such as microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), and other electrical components. The processor may be local to a scanner system that includes the projector, first camera, and second camera, or it may be distributed and may include networked processors. The term processor encompasses any type of computational electronics and may include memory storage elements.

FIG. 12E shows elements of a method 12180 for determining 3D coordinates of points on an object. An element 12182 includes projecting, with a projector, a first uncoded pattern of uncoded spots to form illuminated object spots on an object. FIGS. 12B, 12C illustrate this element 12182 using an embodiment 12100 in which a projector 12110 projects a first uncoded pattern of uncoded spots 12111 to form illuminated object spots 12121 on an object 12120.

A method element 12184 includes capturing with a first camera the illuminated object spots as first-image spots in a first image. This element is illustrated in FIG. 12B using an embodiment in which a first camera 12130 captures illuminated object spots 12121, including the first-image spot 12134, which is an image of the illuminated object spot 12122. A method element 12186 includes capturing with a second camera the illuminated object spots as second-image spots in a second image. This element is illustrated in FIG. 12B using an embodiment in which a second camera 140 captures illuminated object spots 12121, including the second-image spot 12144, which is an image of the illuminated object spot 12122.

A first aspect of method element 12188 includes determining with a processor 3D coordinates of a first collection of points on the object based at least in part on the first uncoded pattern of uncoded spots, the first image, the second image, the relative positions of the projector, the first camera, and the second camera, and a selected plurality of intersection sets. This aspect of the element 12188 is illustrated in FIGS. 12B, 12C using an embodiment in which the processor 12150 determines the 3D coordinates of a first collection of points corresponding to object spots 12121 on the object 12120 based at least in the first uncoded pattern of uncoded spots 12111, the first image 12136, the second image 12146, the relative positions of the projector 12110, the first camera 12130, and the second camera 12140, and a selected plurality of intersection sets. An example from FIG. 12B of an intersection set is the set that includes the points 12112, 12134, and 12144. Any two of these three points may be used to perform a triangulation calculation to obtain 3D coordinates of the illuminated object spot 12122 as discussed herein above in reference to FIGS. 12A, 12B.

A second aspect of the method element 12188 includes selecting with the processor a plurality of intersection sets, each intersection set including a first spot, a second spot, and a third spot, the first spot being one of the uncoded spots in the projector reference plane, the second spot being one of the first-image spots, the third spot being one of the second-image spots, the selecting of each intersection set based at least in part on the nearness of intersection of a first line, a second line, and a third line, the first line being a line drawn from the first spot through the projector perspective center, the second line being a line drawn from the second spot through the first-camera perspective center, the third line being a line drawn from the third spot through the second-camera perspective center. This aspect of the element 12188 is illustrated in FIG. 12B using an embodiment in which one intersection set includes the first spot 12112, the second spot 12134, and the third spot 12144. In this embodiment, the first line is the line 12124, the second line is the line 12126, and the third line is the line 12128. The first line 12124 is drawn from the uncoded spot 12112 in the projector reference plane 12114 through the projector perspective center 12116. The second line 12126 is drawn from the first-image spot 12134 through the first-camera perspective center 12132. The third line 12128 is drawn from the second-image spot 12144 through the second-camera perspective center 12142. The processor 12150 selects intersection sets based at least in part on the nearness of intersection of the first line 12124, the second line 12126, and the third line 12128.

The processor 12150 may determine the nearness of intersection of the first line, the second line, and the third line based on any of a variety of criteria. For example, in an embodiment, the criterion for the nearness of intersection is based on a distance between a first 3D point and a second 3D point. In an embodiment, the first 3D point is found by performing a triangulation calculation using the first image point 12134 and the second image point 12144, with the baseline distance used in the triangulation calculation being the distance between the perspective centers 12132 and 12142. In the embodiment, the second 3D point is found by performing a triangulation calculation using the first image point 12134 and the projector point 12112, with the baseline distance used in the triangulation calculation being the distance between the perspective centers 12134 and 12116. If the three lines 12124, 12126, and 12128 nearly intersect at the object point 12122, then the calculation of the distance between the first 3D point and the second 3D point will result in a relatively small distance. On the other hand, a relatively large distance between the first 3D point and the second 3D would indicate that the points 12112, 12134, and 12144 did not all correspond to the object point 12122.

As another example, in an embodiment, the criterion for the nearness of the intersection is based on a maximum of closest-approach distances between each of the three pairs of lines. This situation is illustrated in FIG. 12D. A line of closest approach 12125 is drawn between the lines 12124 and 12126. The line 12125 is perpendicular to each of the lines 12124, 12126 and has a nearness-of-intersection length a. A line of closest approach 12127 is drawn between the lines 12126 and 12128. The line 12127 is perpendicular to each of the lines 12126, 12128 and has length b. A line of closest approach 12129 is drawn between the lines 12124 and 12128. The line 12129 is perpendicular to each of the lines 12124, 12128 and has length c. According to the criterion described in the embodiment above, the value to be considered is the maximum of a, b, and c. A relatively small maximum value would indicate that points 12112, 12134, and 12144 have been correctly selected as corresponding to the illuminated object point 12122. A relatively large maximum value would indicate that points 12112, 12134, and 12144 were incorrectly selected as corresponding to the illuminated object point 12122.

The processor 12150 may use many other criteria to establish the nearness of intersection. For example, for the case in which the three lines were coplanar, a circle inscribed in a triangle formed from the intersecting lines would be expected to have a relatively small radius if the three points 12112, 12134, 12144 corresponded to the object point 12122. For the case in which the three lines were not coplanar, a sphere having tangent points contacting the three lines would be expected to have a relatively small radius.

It should be noted that the selecting of intersection sets based at least in part on a nearness of intersection of the first line, the second line, and the third line is not used in most other projector-camera methods based on triangulation. For example, for the case in which the projected points are coded points, which is to say, recognizable as corresponding when compared on projection and image planes, there is no need to determine a nearness of intersection of the projected and imaged elements. Likewise, when a sequential method is used, such as the sequential projection of phase-shifted sinusoidal patterns, there is no need to determine the nearness of intersection as the correspondence among projected and imaged points is determined based on a pixel-by-pixel comparison of phase determined based on sequential readings of optical power projected by the projector and received by the camera(s). The method element 12190 includes storing 3D coordinates of the first collection of points.

An alternative method that uses the intersection of epipolar lines on epipolar planes to establish correspondence among uncoded points projected in an uncoded pattern is described in U.S. Pat. No. 9,599,455 ('455) to Heidemann, et al., the contents of which are incorporated by reference herein. In an embodiment of the method described in Patent '455, a triangulation scanner places a projector and two cameras in a triangular pattern. An example of a triangulation scanner 1300 having such a triangular pattern is shown in FIG. 13 . The triangulation scanner 1300 includes a projector 1350, a first camera 1310, and a second camera 1330 arranged in a triangle having sides A1-A2-A3. In an embodiment, the triangulation scanner 1300 may further include an additional camera 1390 not used for triangulation but to assist in registration and colorization.

Referring now to FIG. 14 the epipolar relationships for a 3D imager (triangulation scanner) 1490 correspond with 3D imager 1300 of FIG. 13 in which two cameras and one projector are arranged in the shape of a triangle having sides 1402, 1404, 1406. In general, the device 1, device 2, and device 3 may be any combination of cameras and projectors as long as at least one of the devices is a camera. Each of the three devices 1491, 1492, 1493 has a perspective center O1, O2, O3, respectively, and a reference plane 1460, 1470, and 1480, respectively. In FIG. 14 , the reference planes 1460, 1470, 1480 are epipolar planes corresponding to physical planes such as an image plane of a photosensitive array or a projector plane of a projector pattern generator surface but with the planes projected to mathematically equivalent positions opposite the perspective centers O1, O2, O3. Each pair of devices has a pair of epipoles, which are points at which lines drawn between perspective centers intersect the epipolar planes. Device 1 and device 2 have epipoles E12, E21 on the planes 1460, 1470, respectively. Device 1 and device 3 have epipoles E13, E31, respectively on the planes 1460, 1480, respectively. Device 2 and device 3 have epipoles E23, E32 on the planes 1470, 1480, respectively. In other words, each reference plane includes two epipoles. The reference plane for device 1 includes epipoles E12 and E13. The reference plane for device 2 includes epipoles E21 and E23. The reference plane for device 3 includes epipoles E31 and E32.

In an embodiment, the device 3 is a projector 1493, the device 1 is a first camera 1491, and the device 2 is a second camera 1492. Suppose that a projection point P3, a first image point P1, and a second image point P2 are obtained in a measurement. These results can be checked for consistency in the following way.

To check the consistency of the image point P1, intersect the plane P3-E31-E13 with the reference plane 1460 to obtain the epipolar line 1464. Intersect the plane P2-E21-E12 to obtain the epipolar line 1462. If the image point P1 has been determined consistently, the observed image point P1 will lie on the intersection of the determined epipolar lines 1462 and 1464.

To check the consistency of the image point P2, intersect the plane P3-E32-E23 with the reference plane 1470 to obtain the epipolar line 1474. Intersect the plane P1-E12-E21 to obtain the epipolar line 1472. If the image point P2 has been determined consistently, the observed image point P2 will lie on the intersection of the determined epipolar lines 1472 and 1474.

To check the consistency of the projection point P3, intersect the plane P2-E23-E32 with the reference plane 1480 to obtain the epipolar line 1484. Intersect the plane P1-E13-E31 to obtain the epipolar line 1482. If the projection point P3 has been determined consistently, the projection point P3 will lie on the intersection of the determined epipolar lines 1482 and 1484.

It should be appreciated that since the geometric configuration of device 1, device 2 and device 3 are known, when the projector 1493 emits a point of light onto a point on an object that is imaged by cameras 1491, 1492, the 3D coordinates of the point in the frame of reference of the 3D imager 1490 may be determined using triangulation methods.

Note that the approach described herein above with respect to FIG. 14 may not be used to determine 3D coordinates of a point lying on a plane that includes the optical axes of device 1, device 2, and device 3 since the epipolar lines are degenerate (fall on top of one another) in this case. In other words, in this case, intersection of epipolar lines is no longer obtained. Instead, in an embodiment, determining self-consistency of the positions of an uncoded spot on the projection plane of the projector and the image planes of the first and second cameras is used to determine correspondence among uncoded spots, as described herein above in reference to FIGS. 12B, 12C, 12D, 12E.

FIGS. 15A, 15B, 15C, 15D, 15E are schematic illustrations of alternative embodiments of the projector 1120. In FIG. 15A, a projector 1500 includes a light source, mirror 1504, and diffractive optical element (DOE) 1506. The light source 1502 may be a laser, a superluminescent diode, or a partially coherent LED, for example. The light source 1502 emits a beam of light 1510 that reflects off mirror 1504 and passes through the DOE. In an embodiment, the DOE 11506 produces an array of diverging and uniformly distributed light spots 512. In FIG. 15B, a projector 1520 includes the light source 1502, mirror 1504, and DOE 1506 as in FIG. 15A. However, in the projector 1520 of FIG. 15B, the mirror 1504 is attached to an actuator 1522 that causes rotation 1524 or some other motion (such as translation) in the mirror. In response to the rotation 1524, the reflected beam off the mirror 1504 is redirected or steered to a new position before reaching the DOE 1506 and producing the collection of light spots 1512. In system 1530 of FIG. 15C, the actuator is applied to a mirror 1532 that redirects the beam 1512 into a beam 1536. Other types of steering mechanisms such as those that employ mechanical, optical, or electro-optical mechanisms may alternatively be employed in the systems of FIGS. 15A, 15B, 15C. In other embodiments, the light passes first through the pattern generating element 1506 and then through the mirror 1504 or is directed towards the object space without a mirror 1504.

In the system 1540 of FIG. 5D, an electrical signal is provided by the electronics 1544 to drive a projector pattern generator 1542, which may be a pixel display such as a Liquid Crystal on Silicon (LCoS) display to serve as a pattern generator unit, for example. The light 1545 from the LCoS display 1542 is directed through the perspective center 1547 from which it emerges as a diverging collection of uncoded spots 1548. In system 1550 of FIG. 15E, a source is light 1552 may emit light that may be sent through or reflected off of a pattern generating unit 1554. In an embodiment, the source of light 1552 sends light to a digital micromirror device (DMD), which reflects the light 1555 through a lens 1556. In an embodiment, the light is directed through a perspective center 1557 from which it emerges as a diverging collection of uncoded spots 1558 in an uncoded pattern. In another embodiment, the source of light 1562 passes through a slide 1554 having an uncoded pattern of dots before passing through a lens 1556 and proceeding as an uncoded pattern of light 1558. In another embodiment, the light from the light source 1552 passes through a lenslet array 1554 before being redirected into the pattern 1558. In this case, inclusion of the lens 1556 is optional.

The actuators 1522, 1534, also referred to as beam steering mechanisms, may be any of several types such as a piezo actuator, a microelectromechanical system (MEMS) device, a magnetic coil, or a solid-state deflector.

FIG. 16A is an isometric view of a triangulation scanner 1600 that includes a single camera 1602 and two projectors 1604, 1606, these having windows 1603, 1605, 1607, respectively. In the triangulation scanner 1600, the projected uncoded spots by the projectors 1604, 1606 are distinguished by the camera 1602. This may be the result of a difference in a characteristic in the uncoded projected spots. For example, the spots projected by the projector 1604 may be a different color than the spots projected by the projector 1606 if the camera 1602 is a color camera. In another embodiment, the triangulation scanner 1600 and the object under test are stationary during a measurement, which enables images projected by the projectors 1604, 1606 to be collected sequentially by the camera 1602. The methods of determining correspondence among uncoded spots and afterwards in determining 3D coordinates are the same as those described earlier in FIG. 12 for the case of two cameras and one projector. In an embodiment, the triangulation scanner 1600 includes a processor 1102 that carries out computational tasks such as determining correspondence among uncoded spots in projected and image planes and in determining 3D coordinates of the projected spots.

FIG. 16B is an isometric view of a triangulation scanner 1620 that includes a projector 1622 and in addition includes three cameras: a first camera 1624, a second camera 1626, and a third camera 1628. These aforementioned projector and cameras are covered by windows 1623, 1625, 1627, 1629, respectively. In the case of a triangulation scanner having three cameras and one projector, it is possible to determine the 3D coordinates of projected spots of uncoded light without knowing in advance the pattern of dots emitted from the projector. In this case, lines can be drawn from an uncoded spot on an object through the perspective center of each of the three cameras. The drawn lines may each intersect with an uncoded spot on each of the three cameras. Triangulation calculations can then be performed to determine the 3D coordinates of points on the object surface. In an embodiment, the triangulation scanner 1620 includes the processor 1102 that carries out operational methods such as verifying correspondence among uncoded spots in three image planes and in determining 3D coordinates of projected spots on the object.

FIG. 16C is an isometric view of a triangulation scanner 1640 like that of FIG. 1A except that it further includes a camera 1642, which is coupled to the triangulation scanner 1640. In an embodiment the camera 1642 is a color camera that provides colorization to the captured 3D image. In a further embodiment, the camera 1642 assists in registration when the camera 1642 is moved — for example, when moved by an operator or by a robot.

FIGS. 17A, 17B illustrate two different embodiments for using the triangulation scanner 1 in an automated environment. FIG. 17A illustrates an embodiment in which a scanner 1 is fixed in position and an object under test 1702 is moved, such as on a conveyor belt 1700 or other transport device. The scanner 1 obtains 3D coordinates for the object 1702. In an embodiment, a processor, either internal or external to the scanner 1, further determines whether the object 1702 meets its dimensional specifications. In some embodiments, the scanner 1 is fixed in place, such as in a factory or factory cell for example, and used to monitor activities. In one embodiment, the processor 1102 monitors whether there is risk of contact with humans from moving equipment in a factory environment and, in response, issue warnings, alarms, or cause equipment to stop moving.

FIG. 17B illustrates an embodiment in which a triangulation scanner 1 is attached to a robot end effector 1710, which may include a mounting plate 1712 and robot arm 1714. The robot may be moved to measure dimensional characteristics of one or more objects under test. In further embodiments, the robot end effector is replaced by another type of moving structure. For example, the triangulation scanner 1101 may be mounted on a moving portion of a machine tool.

FIG. 18 is a schematic isometric drawing of a measurement application 1800 that may be suited to the triangulation scanners described herein above. In an embodiment, a triangulation scanner 1101 sends uncoded spots of light onto a sheet of translucent or nearly transparent material 1810 such as glass. The uncoded spots of light 1802 on the glass front surface 1812 arrive at an angle to a normal vector of the glass front surface 1812. Part of the optical power in the uncoded spots of light 1802 pass through the front surface 1812, are reflected off the back surface 1814 of the glass, and arrive a second time at the front surface 1812 to produce reflected spots of light 1804, represented in FIG. 18 as dashed circles. Because the uncoded spots of light 1802 arrive at an angle with respect to a normal of the front surface 1812, the spots of light 1804 are shifted laterally with respect to the spots of light 1802. If the reflectance of the glass surfaces is relatively high, multiple reflections between the front and back glass surfaces may be picked up by the triangulation scanner 1.

The uncoded spots of lights 1802 at the front surface 1812 satisfy the criterion described with respect to FIG. 12 in being intersected by lines drawn through perspective centers of the projector and two cameras of the scanner. For example, consider the case in which in FIG. 12 the element 1250 is a projector, the elements 1210, 1230 are cameras, and the object surface 1270 represents the glass front surface 1270. In FIG. 12 , the projector 1250 sends light from a point 1253 through the perspective center 1258 onto the object 1270 at the position 1272. Let the point 1253 represent the center of a spot of light 1802 in FIG. 18 . The object point 1272 passes through the perspective center 1218 of the first camera onto the first image point 1220. It also passes through the perspective center 1238 of the second camera 1230 onto the second image point 1235. The image points 1200, 1235 represent points at the center of the uncoded spots 1802. By this method, the correspondence in the projector and two cameras is confirmed for an uncoded spot 1802 on the glass front surface 1812. However, for the spots of light 1804 on the front surface that first reflect off the back surface, there is no projector spot that corresponds to the imaged spots. In other words, in the representation of FIG. 12 , there is no condition in which the lines 1211, 1231, 1251 intersect in a single point 1272 for the reflected spot 1204. Hence, using this method, the spots at the front surface may be distinguished from the spots at the back surface, which is to say that the 3D coordinates of the front surface are determined without contamination by reflections from the back surface. This is possible as long as the thickness of the glass is large enough and the glass is tilted enough relative to normal incidence. Separation of points reflected off front and back glass surfaces is further enhanced by a relatively wide spacing of uncoded spots in the projected uncoded pattern as illustrated in FIG. 18 . Although the method of FIG. 18 was described with respect to the scanner 1, the method would work equally well for other scanner embodiments such as the scanners 1600, 1620, 1640 of FIGS. 16A, 16B, 16C, respectively.

Measurement devices, such as the triangulation scanners described herein (see, e.g., FIGS. 11A-18 ), are often used in the inspection of objects to determine whether the object is in conformance with specifications. When objects are large, such as with automobiles for example, these inspections may be difficult and time consuming. To assist in these inspections, sometimes non-contact three-dimensional (3D) coordinate measurement devices are used in the inspection process. An example of such a measurement device is a 3D laser scanner time-of-flight (TOF) coordinate measurement device. A 3D laser scanner of this type steers a beam of light to a non-cooperative target such as a diffusely scattering surface of an object (e.g., the surface of the automobile). A distance meter in the device measures a distance to the object, and angular encoders measure the angles of rotation of two axles in the device. The measured distance and two angles enable a computing device (e.g., the computing device 1910 of FIGS. 19A and 19B) to determine the 3D coordinates of the target. Such scanning can be performed by a modular inspection system, for example, as shown in FIGS. 19A and 19B.

For example, FIG. 19A depicts a modular inspection system 1900 according to an embodiment. FIG. 19B depicts an exploded view of the modular inspection system 1900 of FIG. 10A according to an embodiment. The modular inspection system 1900 includes frame segments that mechanically and electrically couple together to form a frame 1902.

The frame segments can include one or more measurement device link segments 1904 a, 1904 b, 1904 c (collectively referred to as “measurement device link segments 1904”). The frame segments can also include one or more joint link segments 1906 a, 1906 b (collectively referred to as “joint link segments 1906”). Various possible configurations of measurement device link segments and joint link segments are depicted and described in U.S. Patent Publication No. 2021/0048291, which is incorporated by reference herein in its entirety.

The measurement device link segments 1904 include one or more measurement devices. Examples of measurement devices are described herein and can include: the triangulation scanner 1101 shown in FIGS. 11A, 11B, 11C, 11D, 11E; the triangulation scanner 1200 a shown in FIG. 12A; the triangulation scanner 1300 shown in FIG. 13 ; the triangulation scanner 1600 shown in FIG. 16A; the triangulation scanner 1620 shown in FIG. 16B; the triangulation scanner 1640 shown in FIG. 16C; or the like.

In the illustrated embodiment of FIG. 19A, the measurement devices of the measurement device link segments 1904 are triangulation or area scanners, such as that described in commonly owned U.S. Patent Publication 2017/0054965 and/or U.S. Patent Publication No. 2018/0321383, the contents of both of which are incorporated herein by reference in their entirety. In an embodiment, an area scanner emits a pattern of light from a projector onto a surface of an object and acquires a pair of images of the pattern on the surface. In at least some instances, the 3D coordinates of the elements of the pattern are able to be determined. In other embodiments, the area scanner may include two projectors and one camera or other suitable combinations of projector(s) and camera(s).

The measurement device link segments 1904 also include electrical components to enable data to be transmitted from the measurement devices of the measurement device link segments 1904 to the computing device 1910 or another suitable device. The joint link segments 1906 can also include electrical components to enable the data to be transmitted from measurement devices of the measurement device link segments 1904 to the computing device 1910.

The frame segments, including one or more of the measurement device link segments 1904 and/or one or more of the joint link segments 1906, can be partially or wholly contained in or connected to one or more base stands 1908 a, 1908 b. The base stands 1908 a, 1908 b provide support for the frame 1902 and can be of various sizes, shapes, dimensions, orientations, etc., to provide support for the frame 1902. The base stands 1908 a, 1908 b can include or be connected to one or more leveling feet 1909 a, 1909 b, which can be adjusted to level the frame 1002 or otherwise change the orientation of the frame 1902 relative to a surface (not shown) upon which the frame 1902 is placed. Although not shown, the base stands 1908 a, 1908 b can include one or more measurement devices.

According to one or more embodiments described herein, an object of interest (i.e., an object to be scanned) passes through an opening 1912 formed by the frame 1902. For example, a conveyor (not shown) can pass through the opening 1912. The object of interest is placed on the conveyor, and the conveyor moves the object of interest through the opening 1912 and past the one or more of the measurement device link segments. A scan of the object of interest is performed using one or more of the measurement device link segments 1904. The data collected by the one or more of the measurement device link segments 1904 are combined to create a point cloud. It may be desirable to analyze the point cloud to detect defects (e.g., a displacement of a part (such as a fastener), a scratch on a surface of the object, a dent on the surface of the object, etc.).

However, it may not be known in advance where on the object of interest a defect may be anticipated to occur on the object of interest. Therefore, it can be difficult to define where a region of interest on the object of interest may be where the defect is more likely to occur. Further, when a defect is detected, it may be useful to have more details about the defect. As described herein, for scanners such as the triangulation scanner 1101, a typical 2-sigma noise might be 500 μm at a 500 mm measurement distance. In some applications, it is desirable to have a higher sensitivity for finding defects (e.g., than the 2-sigma noise (e.g., less than 500 μm such as about 300 m)). The one or more embodiments described herein provide for obtaining higher resolution data for a region of interest where a defect is detected by the scan.

According to one or more embodiments described herein, a first scan is performed, such as using the modular inspection system 1900, to generate first scan data. If a defect is detected (which is determined by comparing the scan data to reference data), a region of interest is identified. A second scan of the region of interest is then performed to generate second scan data. The second scan data is higher resolution scan data than the first scan data. The second scan data is then combined with the first scan data to generate a point cloud of the object. By performing the second scan, additional detail of the region of interest can be included in the point cloud, thus improving the point cloud.

According to one or more embodiments described herein, a first scan is performed, such as using the modular inspection system 1900, to generate scan data. If a defect is detected (which is determined by comparing the scan data to reference data), a region of interest is identified. A subset of the scan data associated with the region of interest is then upscaled to generate upscaled scan data. The upscaled scan data is then combined with the scan data to generate a point cloud of the object. By upscaling the subset of the scan data associated with the region of interest, additional detail of the region of interest can be included in the point cloud, thus improving the point cloud.

Turning now to FIGS. 20A and 20B, a system 2000A is shown for defect detection according to one or more embodiments described herein, and a system 2000B is shown for defect detection according to one or more embodiments described herein.

The system 2000A includes scanners 2001, 2002, which may be any of the scanners described herein or the like, which are suitable for scanning an object such as the object 2010. Similarly, the system 2000B includes a scanner 2003, which may be any of the scanners described herein or the like, which are suitable for scanning the object 2010. Data collected by the scanners 2001, 2002, 2003 can be transmitted to the computing device 2030, which can be any suitable device, system, unit, etc. for transmitting, receiving, processing, and/or storing data.

The features and functionality of the computing device 2030, which are described in more detail herein with reference to FIGS. 21-23 , can be implemented as instructions stored on a computer-readable storage medium, as hardware modules, as special-purpose hardware (e.g., application specific hardware, application specific integrated circuits (ASICs), application specific special processors (ASSPs), field programmable gate arrays (FPGAs), as embedded controllers, hardwired circuitry, etc.), or as some combination or combinations of these. According to aspects of the present disclosure, the features and functionality described herein can be a combination of hardware and programming. The programming can be processor executable instructions stored on a tangible memory, and the hardware can include the processing device 2032 for executing those instructions. Thus a system memory (e.g., memory 2034) can store program instructions that when executed by the computing device 2030 to implement the features and functionality described herein. be utilized to include other features and functionality described in other examples herein. These features and functionality of the systems 2000A, 2000B are now described with reference to FIGS. 21-23 .

Turning now to FIG. 21 , a method 2100 for defect detection is shown according to one or more embodiments described herein. As an example, the method 2100 uses multiple scans to generate an improved point cloud to show a detected defect for an object of interest. The method 2100 can be performed by any suitable device or system, such as the computing device 2030 of FIG. 2000A.

At block 2102, a first scanner performs a first scan of an object to generate first scan data. In the example of FIG. 20A, a first scanner 2001 scans an object 2010 (i.e., an object of interest) at a first location 2011 as the object moves along a path 2013 (such as a conveyor belt). The first scanner 2001 captures the first scan data using one or more of the techniques described herein. The first scan data can be images in an example.

At block 2104, a computing device and/or a scanner detects a defect on a surface of the object by analyzing the first scan data to identify a region of interest by comparing the first scan data to reference scan data, the region of interest containing the defect. For example, the computing device 2030 receives the first scan data from the first scanner 2001 via a wired and/or wireless communication protocol directly and/or indirectly (such as via a network). The computing device 2030 compares the first scan data to reference data 2040. The reference data 2040 can include a golden point cloud of a golden object (i.e., an object known to be without defects). The computing device 2030 identifies a region of interest. The region of interest is a portion of the surface of the object that contains the defect.

At block 2106, a second scanner performs a second scan of the region of interest to generate second scan data. The second scan data is higher resolution scan data than the first scan data. In an example, the second scan data is higher resolution because the second scanner is a higher quality scanner. In another example, the second scan data is higher resolution because a distance d2 between the second scanner 2002 and the object 2010 (at the time the second scan is performed at the location 2012) is less than a distance d1 between the first scanner 2001 and the object 2010 (at the time the first scan is performed at the location 2011).

According to an example, the first scanner 2001 and the second scanner 2002 are different scanners. In such cases, the first scanner 2001 can be the same type of scanner as the second scanner 2002 or a different type of scanner as the second scanner 2002. According to one or more embodiments described herein, the distance d1 between the object 2010 and the first scanner 2001 is greater than the distance d2 between the object 2010 and the second scanner 2002. This enables the second scan to generate higher resolution second scan data relative to the first scan data. According to one or more embodiments described herein, the object 2010 is moved passed the first scanner 2001 along the path 2013 at a first speed while performing the first scan, and the object 2010 is moved passed the second scanner along the path 2013 at a second speed while performing the second scan. In such cases, the second speed is slower than the first speed, which enables the second scan to generate higher resolution second scan data relative to the first scan data.

In another example, the first scanner 2001 and the second scanner 2002 are the same scanner. In such an example, the first scanner 2001 is moved closer to the object 2010 prior to performing the second scan. That is, the distance d1 between the first scanner 2001 is decreased before performing the second scan with the first scanner 2001.

At block 2108, the computing device combines the first scan data and the second scan data to generate a point cloud of the object. Combining the data to generate the point cloud can be performed by the computing device 2030 or another suitable device or system.

Turning now to FIG. 22 , a method 2200 for defect detection is shown according to one or more embodiments described herein. As an example, the method 2200 uses artificial intelligence to generate an improved point cloud to show a detected defect for an object of interest. The method 2200 can be performed by any suitable device or system, such as the computing device 2030 of FIG. 2000A. In this example, the computing device 2030 includes an upscaling engine 2036 to perform upscaling of scan data. The upscaling engine 2036 can be computer readable instructions stored on the memory 2034, for example.

At block 2202, a scan of an object of interest is performed to generate scan data. For example, the scanner 2003 performs a scan of the object 2010.

At block 2204, a defect on a surface of the object is detected by analyzing the scan data to identify a region of interest by comparing the scan data to reference scan data. The region of interest contains the defect. For example, the computing device 2030 receives the scan data from the first scanner 2003 via a wired and/or wireless communication protocol directly and/or indirectly (such as via a network). The computing device 2030 compares the scan data to the reference data 2040. The reference data 2040 can include a golden point cloud of a golden object (i.e., an object known to be without defects). The computing device 2030 identifies a region of interest. The region of interest is a portion of the surface of the object that contains the defect.

At block 2206, a subset of the scan data associated with the region of interest is upscaled to generate upscaled scan data. For example, the computing device 2030 at block 2204 identifies a region of interest that contains a defect. Data associated with the region of interest is then fed to the upscaling engine 2036, which upscales that data according to the techniques disclosed herein. For example, the upscaling engine 2036 performs at least a portion of the method 500 of FIG. 5 to perform the upscaling.

At block 2208, the computing device combines the scan data and the upscaled scan data to generate a point cloud of the object. Combining the data to generate the point cloud can be performed by the computing device 2030 or another suitable device or system.

Turning now to FIG. 23 , a method 2300 for defect detection is shown according to one or more embodiments described herein. The method 2300 can be performed by any suitable device or system, such as the computing device 2030 of FIGS. 2000A, 2000B.

At block 2301, a scan of a golden reference object is performed to obtain reference data 2040. The golden reference object is an object deemed to be of acceptable quality in that it is known to contain no defects or that any defects are negligible.

At block 2302, a first scan of an object of interest ins performed to obtain first scan data. The scan is performed using one or more of the scanners as described herein or the like.

At block 2304, the first scan data is compared to the reference data. This comparison detects a defect on a surface of the object by analyzing the first scan data to identify a region of interest by comparing the first scan data to reference scan data.

At block 2306, it is determined whether the region of interest is known. For example, this determination evaluates whether the coordinates of the region of interest known. This can be accomplished using markers or other indicia on the surface of the object that is scanned. Such markers or indicia have known coordinates.

If, at decision block 2306, it is determined that the region of interest is known, the method 2300 continues to block 2308, and a second scan is performed of the region of interest as described herein. For example, a second scanner can be used to perform the second scan at a closer distance than the first scan, at a slower speed than the first scan, etc. This results in higher resolution scan data about the region of interest. At block 2310, the first scan data is combined with the second scan data to generate a point cloud of the object.

If, at decision block 2306, it is determined that the region of interest is not known, coordinates of the defect(s) are extracted at block 2312. For example, the scan data can include coordinates of the defect relative to a known origin. In examples, the coordinates are 3D coordinates having the form (x, y, z). Extracting the coordinates can be performed by an AI-based algorithm that is continuously learning and can improve its efficacy over time to find defects. One example of such an AI-based algorithm is the ResNet architecture, although other algorithms are also possible. At block 2314, the coordinates can be transformed to second coordinates known to a second scanner (e.g., the scanner 2002 of FIG. 20A). For example, the second scanner has a separate known origin (separate from the known origin of the first scanner (e.g., the scanner 2002)). The coordinates of the defects are converted to second coordinates known to the second scanner at block 2314. At block 2316, a second scan is performed by the second scanner based on the second coordinates so that the second scanner focuses its scan on the region of interest. At block 2310, the first scan data is combined with the second scan data to generate a point cloud of the object.

According to one or more embodiments described herein, performing a second scan of the region of interest (e.g., the method 2100) and/or upscaling data (e.g., the method 2100) provides an improved point cloud of detected defects on scanned objects. These approaches are faster than scanning the entire object at a higher resolution. According to one or more embodiments described herein, providing higher resolution scan data in the combined point cloud (either by performing a second scan of the region(s) of interest or by upscaling the first scan data for the region(s) of interest) at the regions of interest saves scanning time, reduces the size of the point cloud, and increases the confidence of the data in the region(s) of interest. Moreover, the combined point cloud can be more efficiently visualized, such as using augmented reality, because the point cloud is smaller in size than a point cloud of a high-resolution scan of the entire object, and because the regions of interest have a higher resolution than the first scan produces.

In one or more embodiments, a machine learning model can be used to extract a feature from a point cloud for defects. For example, a CNN can be used to perform feature extraction. When the machine learning model has gained sufficient confidence in determining defects, it can be used to locate defects in point cloud libraries (3D data).

Terms such as processor, controller, computer, DSP, FPGA are understood in this document to mean a computing device that may be located within an instrument, distributed in multiple elements throughout an instrument, or placed external to an instrument.

While embodiments of the invention have been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the embodiments of the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the embodiments of the invention are not to be seen as limited by the foregoing description but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A method comprising: performing a first scan of an object to generate first scan data; detecting a defect on a surface of the object by analyzing the first scan data to identify a region of interest containing the defect by comparing the first scan data to reference scan data; performing a second scan of the region of interest containing the defect to generate second scan data, the second scan data being higher resolution scan data than the first scan data; and combining the first scan data and the second scan data to generate a point cloud of the object.
 2. The method of claim 1, wherein the first scan is performed using a first scanner, and wherein the second scan is performed using the first scanner.
 3. The method of claim 2, further comprising: prior to performing the second scan using the first scanner, decreasing a distance between the first scanner and the object.
 4. The method of claim 1, wherein the first scan is performed using a first scanner, and wherein the second scan is performed using a second scanner.
 5. The method of claim 4, wherein the object is moved passed the first scanner at a first speed while performing the first scan, and wherein the object is moved passed the second scanner at a second speed while performing the second scan, the second speed being slower than the first speed.
 6. The method of claim 4, wherein the object is a first distance from the first scanner when the first scan is performed and a second distance from the second scanner when the second scan is performed, wherein the first distance is greater than the second distance.
 7. The method of claim 4, wherein the first scanner is a first type of scanner, and wherein the second scanner is a second type of scanner different than the first type of scanner.
 8. A method comprising: performing a scan of an object to generate scan data; detecting a defect on a surface of the object by analyzing the scan data to identify a region of interest containing the defect by comparing the scan data to reference scan data; upscaling a subset of the scan data associated with the region of interest containing the defect to generate upscaled scan data; and combining the scan data and the upscaled scan data to generate a point cloud of the object.
 9. The method of claim 8, wherein the upscaling comprises: performing, by a processing device, using a neural network, pattern recognition on the subset of the scan data to recognize a feature in the subset of the scan data; and performing, by the processing device, upscaling of the subset of the scan data to increase a resolution of the subset of the scan data while maintaining the feature to generate the upscaled scan data.
 10. The method of claim 9, further comprising: training the neural network, using a training set of images, to perform the pattern recognition and the upscaling.
 11. The method of claim 10, wherein each set of the training set of images comprises an original image of a laser projection pattern and a downscaled image of the laser projection pattern.
 12. The method of claim 11, wherein the training further comprises: comparing the downscaled image to the original image.
 13. The method of claim 9, wherein the processing device is disposed in a three-dimensional scanner such that performing the pattern recognition and performing the upscaling are performed by the three-dimensional scanner.
 14. The method of claim 9, wherein the neural network comprises an encoder and a decoder.
 15. The method of claim 9, wherein the neural network utilizes a long short-term memory.
 16. The method of claim 9, wherein the feature is at least one of a pattern, a color, or a shape.
 17. The method of claim 8, further comprising: training a neural network to perform upscaling the scan data captured by a three-dimensional triangulation scanner; capturing the scan data using the three-dimensional triangulation scanner; performing, using the neural network, pattern recognition on the scan data; and performing, using the neural network, upscaling on the scan data without manipulating image data associated with the scan data to generate an upscaled image.
 18. The method of claim 17, wherein capturing the image comprises scanning, by the three-dimensional triangulation scanner, an environment.
 19. The method of claim 17, wherein training the neural network comprises using a training set of images.
 20. The method of claim 19, wherein each set of the training set of images comprises an original image of a laser projection pattern and a downscaled image of the laser projection pattern. 